1. Field of the Invention
The present invention relates to a light guide plate and a display device. More specifically, the present invention relates to a light guide plate formed on its surface with a plurality of protrusions each having a cross-section shape that a width is made gradually narrower with a pitch shorter than a wavelength of a light, and a display device provided with the light guide plate.
2. Description of the Prior Art
As a display device provided with a light guide plate, there is, for example, a liquid crystal display device 1 shown in FIG. 13. The liquid crystal display device 1 includes a linear light source 2, a light guide plate 3 placed in a state one side surface 3a thereof is along a longitudinal direction (a front and back direction of the paper in FIG. 13) of the linear light source 2 and a reflective type liquid crystal panel 4 placed below a lower surface 3b of the light guide plate 3.
The light guide plate 3 is, on its upper surface 3c, formed with a number of linear prisms 5 in parallel with the side surface 3a. Each of the prisms 5, 5, . . . has a chevron-shape in cross-section in a longitudinal direction, and each slope 5a away from the side surface (right side in FIG. 13) out of two slopes 5a and 5b forming each prism functions as a reflecting surface. More specifically, a light incident on the light guide plate 3 from the linear light source 2 through the side surface 3a is reflected by each of the reflecting surfaces 5a and emitted from the lower surface 3b of the light guide plate 3 as shown by a dotted arrow 6 in FIG. 13. Then, the emitted light is irradiated onto the liquid crystal panel 4, reflected upwardly by a reflecting layer 4a provided at a bottom of the liquid crystal panel 4, and then emitted from the upper surface (prism surface) 3c through the light guide plate 3.
However, when the light reflected by the above-described reflecting surface 5a is emitted from the lower surface 3b, a part of the light is reflected (Fresnel-reflected) by the lower surface 3b as shown by one dotted arrow 6a in FIG. 13 and emitted from the upper surface 3c without passing through the liquid crystal panel 4. Thereupon, in the light emitted from the upper surface 3c there are, in a mixed manner, a light 6 originally passing through the liquid crystal panel 4 and a light 6a not passing through the liquid crystal panel 4, and consequently, it causes a so-called white blur and/or a decrease of a contrast of a screen.
Thus, in a prior art (1), forming an antireflection film on the lower surface 3b of the light guide plate 3 decreases an amount of the reflected light at the lower surface 3b and thus reduces an influence on image quality due to the reflected light 6a. It is noted that a multi-layered film formed by alternately laminating a low refractive layer formed of a low refractive material such as silicon dioxide (SiO2) and etc. and a high refractive layer formed of a high refractive material such as titanium dioxide (TiO2) and etc. is often utilized as the antireflection film.
On the other hand, as the prior art (2) for decreasing a surface reflection in the above-described optical component, there is known a technique for providing minute concaves and convexes on a surface of an optical component. More specifically, a number of cone-shaped protrusions 7 are formed on a surface of the optical component as shown in FIG. 14, for example. Herein, it is known that if a space of each of the protrusions 7, 7, . . . (corresponding to a diameter of a bottom of each of the protrusions 7), i.e. a pitch Pxe2x80x2 is made smaller than a wavelength of a light transmitted through the optical component, an antireflection effect can be obtained with respect to the light having that wavelength. The antireflection effect is improved as a ratio of a height Hxe2x80x2 to a pitch Pxe2x80x2 of each protrusion 7, i.e., an aspect ratio Sxe2x80x2 (=Hxe2x80x2/Pxe2x80x2) is made large. Accordingly, also by forming these protrusions 7 on the lower surface 3b of the light guide plate 3 in FIG. 13, it is possible to decrease the light reflection by the lower surface 3b and reduce the influence on the image quality due to the reflected light 6a. It is noted that an example of a method for forming these cone-shaped protrusions 7, 7, . . . is disclosed in a Japanese Patent Laying-open No. 2001-272505 [G02B 1/11] laid-open on Oct. 5, 2001.
However, in the prior art (1), there are problems that hermeticity between the light guide plate 3 (lower surface 3b) and the antireflection film is decreased due to a change of an environment such as temperature, humidity and etc. and whereby, the antireflection film is released from the light guide plate 3 and a microcrack is generated on the antireflection film.
On the other hand, in the prior art (2), there is a problem that an antireflection effect cannot be sufficiently exerted. That is, since each protrusion 7 is conical in shape, there necessarily causes clearances 8, 8, . . . shown by oblique lines in FIG. 15 between each of the protrusions 7, 7, . . . . There are problems that an antireflection effect cannot be obtained at these clearances 8, 8, . . . and therefore, a sufficient antireflection effect cannot be obtained at a whole effective area (i.e., an area effectively irradiating a light onto the liquid crystal panel 4) of the lower surface 3b. 
Therefore, it is a primary object of the present invention to provide a novel light guide plate and a display device.
It is another object of the present invention to provide a light guide plate and a display device capable of maintaining high endurance and improving image quality.
A first invention is a light guide plate characterized in that in a light guide plate formed on a surface thereof with a plurality of protrusions each having a cross-section shape that a width is made gradually narrower with a pitch shorter than a wavelength of a light, an interval or space between bases of adjacent protrusions is made uniform.
A second invention is characterized in that in a light guide plate formed on a surface thereof with a plurality of protrusions each having a cross-section shape that a width is made gradually narrower with a pitch shorter than a wavelength of a light, a ratio of a height of each of the plurality of protrusions to the pitch is made more than 1 and a total area of bottoms of the plurality of protrusions to an area of the surface is made more than 90%.
In the first invention, the light guide plate is formed with the plurality of protrusions on its surface. A width of the cross-section of each of the protrusions becomes gradually narrower. Furthermore, the pitch between the protrusions is shorter than the wavelength of the light. On the surface formed with such the protrusions, an antireflection effect can be obtained with respect to the light of the wavelength. In addition, since the interval or space between the bases of the adjacent protrusions is made uniform, the interval or space can be made narrower, that is, the interval or space between the adjacent protrusions can be made smaller. Therefore, it is possible to improve the antireflection effect.
Noted that it is desirable the interval or space described herein is zero. That is, if the protrusions are formed without intervals, a higher antireflection effect can be obtained.
Furthermore, it is desirable that a ratio of the height of each of the plurality of protrusions to the pitch is made more than 1. In this case, if the total area of the bottoms of the plurality of protrusions to the area of the surface formed with the protrusions is made more than 90%, a relatively high antireflection effect can be obtained.
In one embodiment of the present invention, each of the plurality of protrusions is formed in a pyramid shape.
In another embodiment of the present invention, each of the plurality of protrusions is formed in a linear manner.
In the second invention, a restriction that a ratio of the height of each of the plurality of protrusions to the pitch is more than 1 and a restriction that the total area of the bottoms of the plurality of protrusions to the area of the surface is more than 90% are imposed, so that a relatively high antireflection effect can be obtained.
The light guide plates according to these inventions can be applied to a display device.
According to the first invention, since it is possible to make a clearance between adjacent protrusions smaller, it is possible to obtain a higher antireflection effect than in the prior art (2) and to also reduce degradation of image quality due to an undesirable light reflection. In addition, there is no need to provide the antireflection film shown in the prior art (1), it is possible to obtain high endurance. That is, it is possible to improve the image quality while maintaining high endurance.
According to the second invention, since a ratio of the height of each of the protrusions to the pitch is restricted and a total area of the protrusions is restricted, a higher antireflection effect can be obtained than in the prior art (2). Furthermore, there is no need to provide the antireflection film shown in the prior art (1). Consequently, the second invention also yields high endurance and improved image quality.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.